The inducible transcriptional factor NF-?B is a critical mediator of intracellular signaling. It has been linked with cellular response to pro-inflammatory signals and control of the expression of a vast array of genes involved in immune and stress responses, cancer, and apoptosis. While the process of NF-?B activation in the cytoplasm is well understood, little is known regarding the mechanism of NF-?B activation inside the cell nucleus and how NF-?B selectively targets specific genes. We propose to study the mechanisms by which NF-?B is regulated in the cell nucleus in response to oxidative stress. In our recent study, we demonstrated that a human metalloprotein pirin is a nuclear regulator of NF-?B. The long-term objective is to elucidate the regulatory mechanisms by which pirin participates in nuclear regulation of NF-?B. Pirin is a non-heme iron protein expressed in human tissues. We have found that the pirin metal center plays an important role in complex formation between pirin and NF-?B. The ferric, but not ferrous, form of pirin substantially facilities bindin of NF-?B proteins to target ?B genes, which suggests that pirin performs a redox sensing role in NF-?B regulation. We hypothesize that pirin is a nuclear redox sensor protein, the last fortress protecting cells from substantial redox shifting through NF-?B-linked immune defense. Understanding regulation of the inducible transcriptional factor by pirin is thus fundamentally important. We will determine the structural components that control association and dissociation of pirin protein to the NF-?B proteins. We will identify the target signaling genes triggered by human pirin, finally we will perform cellular and in vivo studies to further test the functional relationship between pirin and NF-?B homodimer and heterodimer proteins and how this relationship changes in response to oxidative stress.